Haiti is a tropical climate, with semiarid areas in the eastern mountain areas. The hurricane season lasts from July through October, and the rainy season is from May-July—yet even during this season, the rains are in the evenings for just a couple of hours. November through March sees warm days from around 70-80 degrees (23-32 C) and cooler nights from around 60-70 degrees (15-27C).
The most ideal time to travel to Haiti is during the mild season, which is November through March. Those visiting the hills areas, no matter what the season, will want to bring sweaters and warmer clothing as the nights can become quite cold in the mountainous areas. The air around the water can also get chilly at night, so it's a good idea to bring at least one or two sweaters or sweatshirts for night outings.